Fix pickling of param setters

We now explicitly pickle the fact that they're param setters so that we
can set the flag ParamAccessor at symbol creation, this is necessary
because ParamAccessor is a FromStarts flag.

Since this change isn't binary-compatible, bump TASTY to 6.0.

Author: smarter

compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala

@@ -198,6 +198,7 @@ Standard-Section: "ASTs" TopLevelStat*
                   SCALA2X                             // Imported from Scala2.x
                   DEFAULTparameterized                // Method with default parameters
                   STABLE                              // Method that is assumed to be stable
+                  PARAMsetter                         // A setter without a body named `x_=` where `x` is pickled as a PARAM
                   Annotation
 
   Annotation    = ANNOTATION     Length tycon_Type fullAnnotation_Term
@@ -226,8 +227,8 @@ Standard Section: "Positions" Assoc*
 object TastyFormat {
 
   final val header = Array(0x5C, 0xA1, 0xAB, 0x1F)
-  val MajorVersion = 5
-  val MinorVersion = 1
+  val MajorVersion = 6
+  val MinorVersion = 0
 
   /** Tags used to serialize names */
   class NameTags {
@@ -268,6 +269,7 @@ object TastyFormat {
   // AST tags
   // Cat. 1:    tag
 
+  final val firstSimpleTreeTag = UNITconst
   final val UNITconst = 2
   final val FALSEconst = 3
   final val TRUEconst = 4
@@ -300,6 +302,7 @@ object TastyFormat {
   final val STABLE = 31
   final val MACRO = 32
   final val ERASED = 33
+  final val PARAMsetter = 34
 
   // Cat. 2:    tag Nat
 
@@ -417,15 +420,14 @@ object TastyFormat {
 
   final val HOLE = 255
 
-  final val firstSimpleTreeTag = UNITconst
   final val firstNatTreeTag = SHAREDterm
   final val firstASTTreeTag = THIS
   final val firstNatASTTreeTag = IDENT
   final val firstLengthTreeTag = PACKAGE
 
   /** Useful for debugging */
   def isLegalTag(tag: Int) =
-    firstSimpleTreeTag <= tag && tag <= ERASED ||
+    firstSimpleTreeTag <= tag && tag <= PARAMsetter ||
     firstNatTreeTag <= tag && tag <= SYMBOLconst ||
     firstASTTreeTag <= tag && tag <= SINGLETONtpt ||
     firstNatASTTreeTag <= tag && tag <= NAMEDARG ||
@@ -463,6 +465,7 @@ object TastyFormat {
        | SCALA2X
        | DEFAULTparameterized
        | STABLE
+       | PARAMsetter
        | ANNOTATION
        | PRIVATEqualified
        | PROTECTEDqualified => true
@@ -518,6 +521,7 @@ object TastyFormat {
     case SCALA2X => "SCALA2X"
     case DEFAULTparameterized => "DEFAULTparameterized"
     case STABLE => "STABLE"
+    case PARAMsetter => "PARAMsetter"
 
     case SHAREDterm => "SHAREDterm"
     case SHAREDtype => "SHAREDtype"

compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala

@@ -601,6 +601,7 @@ class TreePickler(pickler: TastyPickler) {
       if (flags is CaseAccessor) writeByte(CASEaccessor)
       if (flags is DefaultParameterized) writeByte(DEFAULTparameterized)
       if (flags is Stable) writeByte(STABLE)
+      if ((flags is ParamAccessor) && sym.isSetter) writeByte(PARAMsetter)
     } else {
       if (flags is Sealed) writeByte(SEALED)
       if (flags is Abstract) writeByte(ABSTRACT)

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -589,6 +589,8 @@ class TreeUnpickler(reader: TastyReader,
           case SCALA2X => addFlag(Scala2x)
           case DEFAULTparameterized => addFlag(DefaultParameterized)
           case STABLE => addFlag(Stable)
+          case PARAMsetter =>
+            addFlag(ParamAccessor)
           case PRIVATEqualified =>
             readByte()
             privateWithin = readType().typeSymbol
@@ -732,11 +734,6 @@ class TreeUnpickler(reader: TastyReader,
               vparamss.nestedMap(_.symbol), name == nme.CONSTRUCTOR)
           val resType = ctx.effectiveResultType(sym, typeParams, tpt.tpe)
           sym.info = ctx.methodType(typeParams, valueParamss, resType)
-          if (sym.isSetter && sym.accessedFieldOrGetter.is(ParamAccessor)) {
-            // reconstitute ParamAccessor flag of setters for var parameters, which is not pickled
-            sym.setFlag(ParamAccessor)
-            sym.resetFlag(Deferred)
-          }
           DefDef(tparams, vparamss, tpt)
         case VALDEF =>
           val tpt = readTpt()(localCtx)